RESOLVED - Coordinate Issue - PAHG Harrisburg PA

Reported Issue:

A customer reported an elevation discrepancy on PAHG between existing NGS benchmarks and the coordinates derived from the use of PAHG. This discrepancy was outside the normal tolerances we would expect.

Issue Resolution:

Upon investigation, it was discovered that a vertical discrepancy of ~ 7 cm existed on the published vs derived coordinates on the control check shots. In looking at the history of the site is was determined that there was a leveling mast adapter with a height of 7.71 cm added to the site on January 26, 2012 as a part of an antenna and receiver update. The appropriate changes were applied to the station coordinates at this time, as the ellipsoid height was changed from 89.32 m to 89.3921 m.

As part of our North American adjustment the coordinates of all stations where recomputed using data that pre-dated the January 26 hardware upgrades on PAHG. When the new NAD83(2011) Epoch 2010.00 coordinates were imported on October 1, 2012 for PAHG the 7.71 cm height offset was not accounted for. Thereby causing the discrepancy that has been reported.

To find a short term solution to this issue, we have recomputed the position of the station using a limited data set to be able to account for the 7.71 cm height offset. This recomputed position will be an interim position until a new position is calculated as part of our bi-annual adjustment that will be completed in the next 30-60 days. Once the larger adjustment has been completed, we will publish a new "permanent" coordinate set for the station, overall change in coordinates should be in millimeter range.

You can find updates to this stations in the SmartNet Site Database - LINK